Fix support of 256 colour palettes.

PuTTY will now correctly redraw it's window when the system palette
changes. In addition the default colours are now at the start of the
palette given to Windows so it's more likely to choose a good colour
when the user is most interested.
Windows font drawing change.

I've finally given up on using the hDC returned by BeginPaint.
Instead the BeginPaint/EndPaint pair is used to fetch the invalidated
rectangle and tell Windows that it's been validated.

After that we get a proper DC for the entire window and use that for
all the drawing.

This allows us to always update the screen immediatly during the WM_PAINT
message processing and avoid all the bugs in other applications that seem
to trip us when we assume the clip region that BeginPaint sets up is okay.

The end result is that it appears to be much more reliable.

Note, however, we still have the issue that windows is getting slower.
The proportional font update and the do_pint change should help.
Don't let do_paint eat too much CPU
Remove unneeded special case code for proportional fonts.

Proportional fonts used to be too unpredictable to print as strings of
characters because they would frequently spread across multiple cells.
With the change to terminal.c that ensures that text strings will be
completely redrawn when any part is changed this is no longer a problem.

This means that using proportional fonts is now the same speed as fixed
width ones so there's no downside to using a fixed width font that's
stored in a truetype font because it also contains CJK characters.

Prime example is the GNU unifont.

True proportional fonts will now display a little differently, but no
more ugly.